The presently disclosed subject matter is related to the subject matter disclosed in U.S. patent application Ser. No. 12/793,317 filed on Jun. 3, 2010 and U.S. patent application Ser. No. 12/901,485 filed on Oct. 8, 2010, which are both co-owned by the present Applicant. The disclosures of both of these related U.S. patent applications are hereby incorporated in their entirety by reference.
Conventionally, vehicle headlamps have been required to have an improved brightness during nighttime driving in order for a driver to be able to drive a vehicle in the same manner as if during daytime driving. In order to cope with the demand, various headlamps having improved optical systems while employing a high intensity light source such as halogen lamps, HID lamps, and the like which have been proposed. (See, for example, Japanese Patent Application Laid-Open Nos. 2007-59162 and Hei 11-273407).
Incidentally, in order to design an improved vehicle headlamp, various visual characteristics should be taken into consideration, wherein the visual characteristics are characterized by, for example, visual cells including cones concentratively distributed at the center of a retina for sensing color at the center of field of vision in a bright environment and rods distributed over a retina except for the center area thereof for sensing light in a dark environment, central vision and peripheral vision, the color matching functions, the relative luminous efficiency curve, and the like. (See FIGS. 56 to 59.) This is because the visibility (noticeability) for pedestrians, roadside obstructs, and the like in actual traffic environments may be affected by these visual characteristics.
If the vehicle headlamps are improved by supplying the lamp with a greater power to be lit with an increased light intensity, it would put the clock back because of the social trend with regard to the environmental concerns. Furthermore, it would be far from the improvement in safety by increasing the visibility (noticeability) for pedestrians, roadside obstructs, and the like in actual traffic environments with effective countermeasures.